When you create a new field, it will take its label text from the field name.
In addition to this, the first letter is capitalised, and underscore characters are replaced with spaces. So the field date_of_birth will have field label 'Date of birth' by default.
You can change the label text of a field by double clicking on the field control's label text in the WYSIWYG panel. You can also change the label text in the Properties tab when the field is selected.
Note that label text is a property of a field and not its field control
You can show or hide a field control's label text in its Properties tab when you have it selected.